Molded articles made from cycloolefin polymers such as thermoset poly(dicyclopentadiene), the preparation of which is described in U.S. Pat. No. 4,400,340, are typically painted with a topcoat such as a white acrylic-urethane enamel. It has been found that a brown stain, attributed to the antioxidant used in the polymer, migrates through the paint film. The antioxidant stain discolors the painted article and is objectionable for cosmetic reasons.